Wafer transfer method performed with vapor thin film growth system and wafer support member used for this method

ABSTRACT

There is provided a wafer transfer method, by which, when a wafer is loaded into a system, heat shock applied to the wafer can be relieved, the frequency of occurrence of crystal dislocation such as slip can be decreased, and productivity can be improved due to saving of energy and time required for heating and cooling of the system, and there is also provided a wafer support member used for this method. In this method, a step for transferring wafers so as to replace a wafer, which finishes its thin film growth process, with a following wafer, which is to be subjected to its thin film growth process, is carried out under the temperature being higher than the room temperature, while the wafer  1  is transferred integrally with a wafer support member  2  used for the thin film growth process.

FIELD OF THE INVENTION

[0001] This invention relates to a wafer transfer method performed witha vapor thin film growth system and also to a wafer support member usedfor this method. More particularly, this invention relates to a wafertransfer method performed in a step for transferring wafers so as toreplace a treated wafer with a following wafer to be treated in a thinfilm growth process with a continuous single wafer processing vapor thinfilm growth system, in which each wafer of a semi-conductor such as asilicone substrate is continuously treated sheet by sheet, and thisinvention relates also to a wafer support member used for this method.

BACKGROUND OF THE INVENTION

[0002] Lately, in the field of semi-conductor industry, a single waferprocessing system is applied widely, due to its many characteristics,comparing with batch processing system.

[0003] For example, a single wafer processing epitaxial film growthsystem is necessary for the deposition process of a thin film such as anepitaxial film and a CVD film for each wafer having an increaseddiameter, because in the resultant film, in-plane characteristics arestable.

[0004] Particularly, in these days, automation technology for replacinga treated wafer with a following wafer to be treated has been improvedso that throughput has been further advanced. Therefore, the singlewafer processing vapor thin film growth system, where each wafer can becontinuously treated sheet by sheet, has been applied generally.

[0005] Will be explained this conventional single wafer processing vaporthin film growth system. For example, as shown in FIG. 4, theconventional system includes, at the upper portion of its reactor 40,usually plurality of gas inlets 47, through which feed gas and carriergas are introduced into the reactor 40; and a flow adjusting plate 48provided with plurality of apertures 48 a, through which the gas flow isadjusted. The conventional system also includes, below this flowadjusting plate 48, a wafer holder section B, into which a wafer 41 isloaded; a rotation axis 49, around which the wafer holder section B isrotated; and a heater 43. Additionally, a motor (not shown), by whichthe above rotation axis 49 is driven to rotate; usually plurality of gasoutlets 50, through which exhaust gas containing unreacted gas from thereactor 40 is discharged; and a controller (not shown) for these gasoutlets are connected to the lower section of the reactor, usually inthe vicinity of the reactor's bottom.

[0006] Further, as shown in an enlarged sectional view of FIG. 5, thewafer holder section B, into which the wafer 41 is loaded, includes, forexample, a wafer support member 42, which has a recess 42 a formed onits upper surface for placing the wafer; and a lifting pin 44, which isused when the wafer 41 is placed on and removed from the above recess 42a.

[0007] In the single wafer processing vapor thin film growth system,which continuously treats each wafer sheet by sheet, a wafer, whichfinishes its thin film growth process, is replaced with a followingwafer, which is to be subjected to its thin film growth process, underthe temperature being generally higher than the room temperature. Thatis to say, this wafer replacing operation is carried out under thetemperature being more closer to the temperature for the growth of thethin film, which allows the wafer to be cooled and heated in short time,resulting in quick growth of the thin film.

[0008] However, in this case, large temperature gap is generated betweenthe wafer, which is introduced into the reactor under the roomtemperature, and the wafer support member, which is already heated inthe reactor. Then, when the wafer is brought into contact with the wafersupport member, temperature gap is generated in the wafer. Accordingly,if the wafer is directly supported on the wafer support member, heatshock will be produced in the wafer due to the wafer's temperature gap.As a result, since this heat shock may cause crystal defect such asstrain and slip dislocation, damage may be caused in the wafer.

[0009] In order to solve such problem, for example, in the conventionalvapor thin film growth process, after the wafer is introduced into thereactor, an operation is carried out, where the wafer is pre-heated onthe lifting pin so that the temperature gap between the wafer and thewafer support member is decreased.

[0010] This pre-heating operation will be explained closely, referringto FIG. 5. The wafer 41 is loaded into the reactor 40 by a loading andunloading robot 45. The loaded wafer 41 is lifted so as to be locatedabove the heater 43 by the lifting pin 44. Then, the wafer 41 ispre-heated for the predetermined time until the temperature gap betweenthe wafer and the wafer support member becomes to fall within thepredetermined temperature range, and the wafer is placed on the recess42 a.

[0011] In the above conventional vapor thin film growth process, duringthe growth of the thin film, impurities are attached to not only thewafer but also to the wafer support member 42 having an exposed surfaceto the reactive gas. Then, during the operation of the single waferprocessing vapor thin film growth system, some of impurities attached tothe wafer support member are released therefrom and contaminate thewafer. Therefore, in the conventional method, such impurities should beremoved periodically.

[0012] As stated above, in the conventional vapor thin film growthprocess, after loading the wafer into the reactor, the wafer ispre-heated on the lifting pin in order to decrease the temperature gapbetween the wafer and the wafer support member. However, due to distancebetween the heater and the wafer held on the lifting pin, it takes longtime to heat the wafer, which delays the growth of the thin film.

[0013] Further, the recess is usually formed on the surface of the wafersupport member for placing the wafer, which means that the wafer supportmember has thickness difference between its central portion and itsperipheral portion. This generates a heat capacity gap between thecentral portion and the peripheral portion in the wafer support member.

[0014] In this connection, at the moment when the wafer is supported onthe wafer support member or during heating of the wafer, temperature gaptends to be generated also in the wafer between its outer peripheralarea and its central area, because its outer peripheral area is broughtinto contact with the peripheral portion of the wafer support member,while its central area is not. This temperature gap generated in thewafer causes crystal dislocation such as slip.

[0015] Additionally, in order to remove the impurities attached to thewafer support member, the thin film growth process for each wafer shouldbe shut down temporally for cleaning the wafer support member and afterthat, the process should be started again. As a result, theavailability, i.e., productivity of the system is lowered, which resultsin high cost in performing the conventional thin film growth process.

SUMMARY OF THE INVENTION

[0016] The present invention is attained in order to solve the abovetechnical problems and has an object to provide a wafer transfer methodwhich can relieve heat shock applied to each wafer loaded into a systemso that crystal dislocation such as slip can be decreased and which cansave energy and time required for heating and cooling the system so thatthe productivity is improved, and provide also a wafer support memberused for this method.

[0017] Another object of the present invention is to provide a wafertransfer method, in which impurities can be removed from a wafer supportmember outside of the vapor thin film growth system without shuttingdown the thin film growth process so that the productivity of thissystem can be improved.

[0018] In accordance with one aspect of the present invention, there isprovided a wafer transfer method performed with a continuous singlewafer processing vapor thin film growth system, in which each wafer iscontinuously treated sheet by sheet and heated from its back side, themethod comprising a step for transferring wafers so as to replace awafer, which finishes its thin film growth process, with a followingwafer, which is to be subjected to its thin film growth process, underthe temperature being higher than the room temperature, while the waferis transferred integrally with a wafer support member used for the thinfilm growth process.

[0019] In one preferred embodiment of the above wafer transfer method inaccordance with the present invention, the step for transferring wafersso as to replace them is carried out under the temperature of 500° C. to1000° C. in the system.

[0020] In another preferred embodiment of the above wafer transfermethod in accordance with the present invention, the above wafer supportmember is fabricated from the same material of the wafer, and in stillanother preferred embodiment, a recess is formed on the above wafersupport member for placing the wafer so that the depth of the recess hassubstantially the same dimension as the thickness of the wafer.

[0021] In another preferred embodiment of the present invention, eachwafer subjected to the above thin film growth process is a siliconewafer.

[0022] Finally, in accordance with another aspect of the presentinvention, there is provided a wafer support member used for a thin filmgrowth process, the member being fabricated from the same material of awafer subjected to the thin film growth process and having a recess forplacing the wafer so that the depth of the recess has substantially thesame dimension as the thickness of the wafer.

[0023] The wafer transfer method in accordance with the presentinvention is characterized with that the wafer is transferred integrallywith the wafer support member used for the thin film growth processperformed with the single wafer processing vapor thin film growthsystem. If only the wafer is directly loaded into the heated reactorwithout the wafer support member, heat shock will be produced there dueto the wafer's temperature gap. However, in the present invention, thewafer is supported in the wafer support member and loaded integrallyinto the reactor as they are. Therefore, damage, which might be causedby the above heat shock, can be decreased.

[0024] Additionally, the treated wafer can be replaced with thefollowing wafer to be treated under higher temperature, resulting inthat the thin film growth process can be carried out more quickly.

[0025] Further, the wafer support member can be fabricated from the samematerial of the wafer and the depth of the recess formed on the wafersupport member can have substantially the same dimension as thethickness of the wafer. Accordingly, the total thickness, which isobtained by adding the thickness of the wafer to the thickness of thewafer support member while the wafer is supported on the wafer supportmember, becomes to be uniform throughout the global surface of thewafer. Therefore, when the wafer is supported on the wafer supportmember, the temperature gap in the wafer between its central area andits peripheral area, which might be caused by the wafer's partial heatcapacity gap, can be decreased to the minimum value.

[0026] Finally, the impurities attached to the wafer support member canbe removed outside of the vapor thin film growth system, hence, the thinfilm growth process for the wafer is not required to be shut down forevery removing operation, which leads to improved productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a schematic cross sectional view showing theconstruction of a wafer holder section in a single wafer processingvapor thin film growth system in accordance with the present invention;

[0028]FIG. 2 is a graph showing two curves, temperature vs. time at thecentral area and at the peripheral area in the wafer supported on thewafer support member during heating and cooling in a conventional vaporthin film growth process performed with a conventional single waferprocessing vapor thin film growth system;

[0029]FIG. 3 is a graph showing two curves, temperature vs. time at thecentral area and at the peripheral area in the wafer supported on thewafer support member during heating and cooling in a vapor thin filmgrowth process where a wafer transfer method in accordance with thepresent invention is performed with a single wafer processing vapor thinfilm growth system in accordance with the present invention;

[0030]FIG. 4 is a schematic cross sectional view showing the structureof a reactor of a conventional single wafer processing vapor thin filmgrowth system; and

[0031]FIG. 5 is a schematic cross sectional view showing the structureof a wafer holder section of a conventional single wafer processingvapor thin film growth system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Now, the present invention will be explained more concretely,referring to the accompanied drawings. In the following description, thepresent invention will be explained with an embodiment of siliconeepitaxial film growth for each silicone wafer. However, the applicationfield of the present invention is not limited to this example.

[0033]FIG. 1 shows an example of a wafer holder section (correspondingto B section in a single wafer processing vapor thin film growth system)in a single wafer processing vapor thin film growth system, where awafer transfer method in accordance with the present invention isperformed.

[0034] In the single wafer processing vapor thin film growth system inaccordance with the present invention, at least one gas inlet and anadjusting plate are provided in the upper portion of a reactor, andbelow the adjusting plate, a wafer holder section, a holder rotationaxis and a heater are provided. Then, a motor, at least one gas outletand their controller are provided in the lower portion (usually in thevicinity of the bottom) of the reactor. The above wafer holder sectionincludes a wafer support member 2 (42 in FIGS. 4 and 5), a lifting pin 4(44 in FIGS. 4 and 5) and a bearing member 6. In this connection, thesingle wafer processing vapor thin film growth system in accordance withthe present invention is configured in the same manner as theconventional system (See FIGS. 4 and 5).

[0035] However, the system of the present invention is different fromthe conventional system in that, first, the lifting pin 4 can lift thewafer 1 integrally with the wafer support member 2, while the wafer 1 issupported in the wafer support member 2, and next, a loading andunloading robot 5 can contain and hold the wafer support member 2integrally with the wafer, while the wafer 1 is supported in the wafersupport member 2.

[0036] Precisely, in the system in accordance with the presentinvention, the wafer 1 is loaded into the reactor through the means ofthe loading and unloading robot 5, while the wafer 1 is supported in thewafer support member 2. Then, the wafer 1 is lifted integrally with thewafer support member 2 by the lifting pin 4, and after the loading andunloading robot 5 is taken away from the reactor, the wafer is locatedat a predetermined position. During this operation, due to temperaturegap between the wafer support member 2 and the bearing member 6 holdingthis member, heat shock is applied to the wafer support member 2, butthe heat shock is not applied to the wafer 1 itself.

[0037] After that, the wafer 1 and the wafer support member 2 are heatedfor a predetermined time to the predetermined temperature.

[0038] In the present invention, the wafer support member 2 may befabricated from a material, which is usually used for this type of wafersupport member, such as graphite, quartz, and silicone. However, it isnot limited to these materials. Particularly, the material, with whichthe wafer support member 2 is fabricated, is preferably same as thematerial (e.g., silicone) of the wafer substrate to be processed. Then,it is particularly prefer that the depth of a recess 2 a, which isformed on the upper surface of the above wafer support member 2 forplacing the wafer, has the substantially same dimension of the thicknessof the wafer substrate 1.

[0039] Precisely, if the wafer 1 is fabricated from the same material ofthe wafer support member 2 and the total thickness obtained by addingthe thickness of wafer 1 to that of the wafer support member 2 is almostuniform throughout the global surface of the wafer 1 during heating ofthe wafer and the wafer support member, the heat capacity is stable inthe wafer support member 2 between its several portions, for examplebetween its central portion and its peripheral portion, while the wafer1 is supported on the wafer support member 2. Accordingly, in the waferbetween its central area and its peripheral area, the temperature gapderived from heating and cooling can be decreased.

[0040] Referring to FIG. 2 (the conventional system) and FIG. 3 (thepresent system), each graph illustrating two curves, temperature vs.time at the central area and at the peripheral area, respectively, inthe wafer supported on the wafer support member. In the case of theconventional system, the wafer support member is fabricated from thematerial (e.g., quartz glass), which is different from the material ofthe wafer to be treated (e.g., silicone). On the other hand, in the caseof the present system, the wafer support material is fabricated from thesame material of the wafer to be treated (e.g., silicone) and the depthof the recess has the same dimension of the thickness of the wafer.Then, the two systems are operated so that the heating and coolingconditions in the reactors are same (That is to say, near the waferholder sections in reactors of these two systems, the almost samepatterns are obtained related to the cooling and heating and to thetime). In each Figure, the continuous line shows the temperature at thecentral area of the wafer, while the dotted line shows the temperatureat the peripheral area of the wafer. By the consideration on the basisof comparison of two graphs FIGS. 2 and 3, it is found that in FIG. 2,there is temperature gap to some degree, but in FIG. 3, there is notsignificant temperature gap. Thus, the above mentioned effect can beconfirmed clearly.

[0041] In the wafer transfer method in accordance with the presentinvention, it is prefer that the step for transferring the wafers so asto replace them is carried out under the temperature of 500° C. to 1000°C.

[0042] If the temperature is below 500° C., during heating and cooling,there will not be significant difference between the present method andthe conventional method in the frequency of occurrence of crystal defectsuch as slip dislocation. Accordingly, one of effects of the presentinvention can not be sufficiently obtained, i.e., slip dislocation orthe like can not be prevented reliably. Additionally, the largetemperature gap leads the delay of heating and cooling operation(decreased productivity) and increased energy consumption.

[0043] On the other hand, if the operation temperature is above 1000°C., the frequency of occurrence of slip dislocation and the like isincreased.

[0044] Conventionally, the thin film growth process on the wafer must beshut down for removing the impurities attached to the wafer supportmember. However, in the present invention, such removing operation canbe carried out outside of the vapor thin film growth system withoutshutting down the thin film growth process. This is a further advantageof the present method.

[0045] For example, in order to remove the silicone film attached to thewafer support member, the wafer support member is dipped into the mixedacid of nitric acid and hydrofluoric acid outside of the vapor thin filmgrowth system without shutting down the thin film growth process.

[0046] Therefore, the availability of the vapor thin film growth systemis further improved comparing with the conventional system, which leadsmuch higher productivity.

EXAMPLE 1

[0047] For a single wafer processing vapor thin film growth system inaccordance with the present invention, a system having the followingstructure was used. Precisely, at least one gas inlet and an adjustingplate are provided in the upper portion of a reactor, and below theadjusting plate, a wafer holder section, a rotation axis of the waferholder section and a heater are provided. At the bottom of the reactor,a motor for driving the rotation axis and at least one gas outlet areprovided. As shown in FIG. 1, the above wafer holder section iscomprised of a wafer support member (fabricated from silicone), whichhas a recess formed on its upper surface for placing the wafer; alifting pin, which is configured so as to load and unload the waferintegrally with the wafer support member, while the wafer is supportedin the support member; and a bearing ring, which holds the wafer supportmember.

[0048] By means of the above system, each silicone wafer having thediameter of φ300 nm was continuously treated sheet by sheet so as tocarry out a silicon epitaxial film growth process.

[0049] The epitaxial film growth process was carried out under thetemperature of 1000° C., while a step for transferring wafers so as toreplace a treated wafer with a following wafer to be treated wasperformed under the temperature of 700° C. in the reactor.

[0050] The frequency of occurrence of slip dislocation of the treatedwafer was evaluated with a differential interference microscope. Theresult is shown in Table 1.

COMPARATIVE EXAMPLE 1

[0051] By means of the conventional single wafer processing vapor thinfilm growth system shown in FIG. 4 (whole system) and FIG. 5 (waferholder section), in the same manner as Example 1, each silicone waferhaving the diameter of φ300 nm was continuously treated sheet by sheetso as to carry out a silicon epitaxial film growth process.

[0052] The epitaxial film growth process was carried out under thetemperature of 1000° C., while in a step for transferring wafers so asto replace a treated wafer with a following wafer to be treated, afterthe wafer to be treated was loaded into the reactor, the wafer waspre-heated to the temperature of 700° C. on the lifting pin.

[0053] The frequency of occurrence of slip dislocation of the treatedwafer was evaluated with a differential interference microscope. Theresult is shown in Table 1. TABLE 1 Frequency of occurrence of slipdislocation of wafer Exampel  0% Comparative Example 1 15%

[0054] As shown in Table 1, in the conventional method wherein thepre-heating is carried out, under the pre-heating temperature of 700°C., the slip dislocation was occurred on the wafer, on the other hand,in the wafer transfer method in accordance with the present invention,even under the wafer's loading and unloading temperature of 700° C., theslip dislocation was not occurred on the wafer.

EXAMPLE 2

[0055] The processes and evaluations related to the frequency ofoccurrence of slip dislocation were carried out in the same way as inExample 1. However, in each process, a step for transferring wafers soas to replace a treated wafer with a following wafer to be treated wasperformed in the reactor under the temperature stated in Table 2. Theresult is shown in Table 2.

COMPARATIVE EXAMPLE 2

[0056] The processes and evaluations related to the frequency ofoccurrence of slip dislocation were carried out in the same way as inComparative Example 1. However, in each process, in a step fortransferring wafers so as to replace a treated wafer with a followingwafer to be treated, the wafer loaded into the reactor was pre-heated tothe temperatures shown in Table 2. The result is shown in Table 2. TABLE2 Wafer's loading and unloading temperature (Pre-heating temperature)500° C. 600° C. 700° C. 800° C. 900° C. 1000° C. 1100° C. Example 2 ◯ ◯◯ ◯ Δ Δ X Comp. ◯ Δ Δ X — — — Example 2

[0057] As shown in FIG. 2, if the wafer's loading and unloadingtemperature or pre-heating temperature was smaller than 500° C., in bothmethods; the wafer transfer method in accordance with the presentinvention and the conventional wafer transfer method accompanied withthe pre-heating operation, the frequency of occurrence of slipdislocation of each wafer was smaller than 10%. That is to say, there isno striking difference between these methods.

[0058] However, if the wafer's loading and unloading temperature orpre-heating temperature was 600° C. to 800° C., the frequency ofoccurrence of slip dislocation was equal to or larger than 10% in theconventional method, on the other hand, it was smaller than 10% in thepresent method. That is to say, the yield of wafer products is improvedin the present invention.

[0059] But even in the method in accordance with the present invention,if the wafer's loading and unloading temperature was equal to or higherthan 900° C., the frequency of occurrence of slip of wafer was equal toor larger than 10%.

EXAMPLE 3

[0060] With the single wafer processing vapor thin film growth systemused in Example 1, by the wafer transfer method in accordance with thepresent invention, a silicone epitaxial film growth process for thesilicone wafer was performed sequentially for 5 days. Then, the averagenumber of treated wafers per day (productivity) was calculated. Theresult is shown in Table 3.

COMPARATIVE EXAMPLE 3

[0061] With the single wafer processing vapor thin film growth systemused in Comparative Example 1, by the same wafer transfer method ofComparative Example 1, a silicone epitaxial film growth process for thesilicone wafer was performed sequentially for 5 days. Then, the averagenumber of treated wafers per day (productivity) was calculated.

[0062] But in order to remove the impurities attached to the wafersupport member, the film growth process with the vapor thin film growthsystem was shut down for about 64 minutes every 3 hours so that etchingwas performed with hydrogen chloride for the wafer support member in thevapor thin film growth system. The result is shown in TABLE 3Productivity (sheets/day) Example 3 206 Comparative Example 3 152

[0063] As shown in Table 3, by the wafer transfer method in accordancewith the present invention, the impurities attached to the wafer supportmember could be removed without the necessity of shut down of theepitaxial film growth process for the wafer. Accordingly, theproductivity is further improved comparing with the conventional method.

[0064] In the single wafer processing vapor thin film growth process,the wafer transfer method in accordance with the present invention canrelieve the heat shock applied to the wafer loaded into the reactor.Therefore, the occurrence of crystal defect such as slip dislocation isdecreased.

[0065] Additionally, in this connection, the loading and unloading ofwafer can be carried out under the high temperature. This enables quickheating and cooling.

[0066] Further, during heating and cooling, the temperature gap betweenseveral areas of the wafer (, particularly between the central area andperipheral area in the wafer,) can be decreased. Accordingly, the wafercan be cooled and heated uniformly throughout the global surface of thewafer.

[0067] Finally, the removing operation of the impurities attached to thewafer support member can be performed outside of the vapor thin filmgrowth system without shutting down the vapor thin film growth process.Therefore, the productivity of the single wafer processing vapor thinfilm growth system can be improved.

What is claimed is:
 1. A wafer transfer method performed with a singlewafer processing vapor thin film growth system, which can continuouslytreat each wafer sheet by sheet and which heats the wafer from its backside surface, said method comprising a step for transferring wafers soas to replace a wafer, which finishes its vapor thin film growthprocess, with a following wafer, which is to be subjected to its vaporthin film growth process, under the temperature being higher than theroom temperature, while said wafer is transferred integrally with awafer support member used for said thin film growth process.
 2. A wafertransfer method according to claim 1, wherein said step for transferringwafers so as to replace them is carried out under the temperature of500° C. to 1000° C.
 3. A wafer transfer method according to claim 1,wherein said wafer support member is fabricated from the same materialof said wafer.
 4. A wafer transfer method according to claim 1, whereinsaid wafer support member has a recess for placing said wafer so thatthe depth of said recess has the substantially same dimension as thethickness of said wafer.
 5. A wafer transfer method according to claim1, wherein said wafer subjected to said thin film growth process is asilicone wafer.
 6. A wafer support member used for a thin film growthprocess, said member being fabricated from the same material of a wafersubjected to said thin film growth process and having a recess forplacing said wafer so that the depth of said recess has thesubstantially same dimension as the thickness of said wafer.
 7. A wafertransfer method according to claim 2, wherein said wafer support memberis fabricated from the same material of said wafer.
 8. A wafer transfermethod according to claim 2, wherein said wafer support member has arecess for placing said wafer so that the depth of said recess has thesubstantially same dimension as the thickness of said wafer.
 9. A wafertransfer method according to claim 2, wherein said wafer subjected tosaid thin film growth process is a silicone wafer.